Partially dehydrated sodium sulphide



Feb. 2, 1-932. 5. B. HEATH PARTIALLY DEHYDRATED SODIUM SULPHIDE Filed March 18. 1929 ZQYarI Fryer l/r/ /d fix 714 2(6 fer INVENTOR. iwlaon .5 flea??? ATTORN 6 Patented Feb. 2, 1932 1 UNITED STATES snnilno 'q rarest errlce B. HEATH, OF MIDLAND, MICHIGAN, ASSIGNOR TO THE DOW CHEMICAL COM- PANY, OF MIDLAND, MICHIGAN, A COR-PQRA'EION OF MICHIGAN I PARTIALLY DEHYDRATED SODIUM SULPHIDE Application filed March 18, 1929.

' The invention relates to improvements in the manufacture of metallic compound s, nor-,

mally containing water of crystallization, in a partially dehydrated, divided, non-coalescent form whereby the particles so obtained exhibit free-flowing characteristics and a reduced tendency tocake or solidify in the containeror package.

Generally speaking, compounds of the character in hand can existin one or more solid hydrated forms containing water of crystallization and are further characterized as being deliquescent substances readily attracting moisture from the air and dissolving easily in water. Such substances on account of their high degree of solubility do not crystallize readily from their aqueous solutions and can be crystallized then only from relatively concentrated solutions. The productso obtained consists of crystals having the surfaces thereof wetted with the concentrated mother liquor. Unless this adhering'mother liquor'is removed the crystals upon standing soon cake or coalesce into a moreor less'solid mass, often difiicult to break up. For obtaining a pure crystalline product in divided form which can be stored in suitable containers or packages without caking or solidifying, it is important to separate the crystals as completely as possible fromany adhering mother liquor. WVashing with water accomplishes this result more or less completely,'but at the expense of redissolving a considerable proportion of the crystals themselves. Ordinary drying methods inmost cases cannot be used without danger of fusing the crystals together into a solid mass.

One method of processing a substance of the present character, as specifically applied Serial No. 347,826.

layer of the substance upon the surface thereof; scraping the solidified layer off in the form of flakes; kiln-drying the product and then cooling in a current of air, whereby the individual flakes are superficially dried or dehydrated further to the point where their inherent tendency to coalesce is materially reduced. The product so obtained is a partially dehydrated divided or comminuted form of the normal hydrated salt.

The present invention comprises an improvement upon the above described method of working whereby a divided or comminuted product having a lower content of water of crystallization is obtained, such'product possessing to an increased degree the desired free-flowing and non-caking characteristics, the particles also being harder and stronger and thereby less susceptible to crumbling or powdering when handled.

A. further advantage lies in the fact that the particles may be prepared by a flaking process wherein the solidified film formed on the surface of the flalrer drum is more easily and cleanly detached therefrom by the scraper knives than by the method as at present employed.

To the accomplishment of the foregoing and related ends, theinvention, then consists of the steps and new products hereinafter fully described and particularly pointed out in the claims, the annexed drawing and following description setting forth certain detailed procedures embodying the invention, these being illustrative, however, of but a few of the various ways in which the principle of my invention may be applied.

In said. annexed drawing: I

The single figure there appearing illustrates in diagrammatic fashion an apparatus arranged for the carrying out of my improved process or method.

In general a' material may be flaked in the manner already described if it can be prepared by evaporation of its solution to a fluid or semi-fluid mass of such composition that,

upon cooling, complete solidification thereof will occur at a temperature materially above normal atmospheric temperature. hen such fluid material 1s applied in a thin n a l film to the cooled surface of a revolving fiaker drum, the film solidifies so that it can be scraped off as well-defined flakes. The higher the solidification temperature thereof, the more easily and rapidly is the operation performed.

The usual practice has been to carry the preliminary evaporation of the solution to be flaked only so far as to maintain a'clear liquid at the boiling temperature, and it has been thought advisable to'stop the concentration short of the point where any material precipitation of solid crystals takes place. I have found, in some cases, that the solidied film formed by chilling such clear solution on a flaker drum is tough and rubbery, adhering tightly to the drum, sothat it can not be easilydetached, and furthermore is not sulficiently hard and brittle to break off cleanly in flakes of regular and definite form. At times and with certain materials the difficulties involvedin producing a satisfactory flake prodnot are of very material consequence.

. I have now found that difficulties of the sort just mentioned maybe largely avoided if the solution tobe flaked contains in appreciableamount solid crystalline particles held in suspension therein; The presence of such particlesin the solidified film as it is formed upon the surface ofthe fiaker drum serves to alter or modify the character of the fihn, imparting; to itgreater hardness and brittleness and also, apparently, accelerating somewhatthe rate of solidification. To obtain the requisite suspension of solid crystalline particles I carry the concentration of the solution further than has been the practice pre viously'and, indeed, to the point where a material precipitation of crystals takes place therein,either atthe temperature of evaporation or when cooled to a certain lower temperature above the solidfying point of the concentrated solution. In other words, the concentration is caused to proceed beyond the point of saturation of the dissolved constituent or of at least one of the dissolved constituents, should more than one be present, at some temperature above that at which the mass will solidify. Proceeding in this way I obtain a slurry, or magma, of'precipitated crystals and hot mother liquor, the consistency of which ispreforably so regulated, by controlling the amount of crystallization, that it may be conveniently pumped through pipes front the concentrating vessel to the flaking apparatus in the usual way.

- Other advantages also accrue as a result of my improved method of procedure. Obviously the flake product so made contains a higher percentage by Weight of the essential constituent. Another advantage is that certain products can be-conveniently prepared in flake form which cannot readily beso made if it'is attempted to flake a clear solution thereof. Furthermore it is frequently of advantage to concentrate under vacuum, whereby a lower final temperature suffices to give the same degree of concentration. Under such procedure, however, the solubility of the dissolved substance in the mother liquor is proportionately lowered and a greater or lesser quantity of crystals is precipitated. By making a crystal slurry in this way and flaying such slurry, instead of fiakin a clear solution of equal concentration, wh ch could be obtained only by evaporating at a higher temperature and correspondingly higher pressure, a notable economy in operation is realized. Concurrently, such procedure often results in lessened wear and tear and corrosion on the evaporating equipment, due to operating a lower temperature.

Taking calcium chloride as an example of a product of the type herein referred to, this salt is now manufactured commercially in large quantity by concentrating a solution thereof to a content of from 71 to 7 5 percent.

of the anyhdrous salt and then flaking and drying in accordance with the patented procedure previously descnbed. The flaked product so obtained contains somewhat less water of crystallization than corresponds tothe dehydrated salt CaCl 2H O, corresponding to about 7 5 per cent. anhydrous 0e01,,

or slightly less.

For proceeding in accordance with the present invention, I concentrate a solution of calcium chloride to a temperature of 177 to 178 C. at atmospheric pressure, whereupon continued ev. poration results in salting out crystals of calcium chloride monohydrate, (32101 1120, forming a slurry thereof with the hot mother liquor, which is then flaked in the usual way. The concentrated solution exhibits a propensity to become superheated if evaporated rapidly, so thatthe temperature during the salting out of the monohydrate crystals may rise to as high as 186 C. if the rate of evaporation is sufficiently high. The slurry has a very sharp freezing point and will solidify at a temperature above 170 to form hard strong particles. A slurry having a consistency such that it can be pumped readily from the concentrator to the flaker will produce a flake containing about 77 per cent. anhydrous calcium chloride, which may then be superficially dried and cooled as already described.

My preferred method of procedure is indicated in the accompanying drawing in which 1 represents a concentrating kettle provided with an agitator 2 and heating coils 3.- Calcium chloride solution is fed in by. way of pipe 4. Concentration in this kettle. is either continuous or by batches as preferred, there be-.

5 and it may be either fed directly into the pan of the flaker or distributed upon the drum by means of a suitable spreading device indicated at 6. The revolving flaker drum 5 is cooled in the ordinary way and there is formed thereon a thin solidified film of the chloride which is scraped ofi" by the knife 7 and delivered to the conveyor 8 and thence to the dryer 9 shown as of the rotary kiln type. The latter is preferably provided with internal shovels for lifting and dropping the flakes through a heated gaseous current derived from the combustion of fuel in the connected furnace 10, such heated gaseous ourrent being drawn through the dryer by the exhauster 11 and discharged at 12. The hot superficially dried flakes are discharged from the dryer 9 to conveyor 13 which delivers them to the cooler 14, here shown as of similar construction to the dryer. A current of air is drawn through the cooler by the exhauster fan 15, in the direction as indicated by the. arrows at 16 and 17. The dried and cooled flakes are discharged to the conveyor 18 to be delivered to the packaging or other further step in the treatment.

The product from the flaker so obtained, contains, as previously pointed out, a higher percentage of anhydrous CaCI than that prepared by present" methods, i. e. 77 per cent. as compared with from 71 to 7 5 per cent. CaCl It consists essentially of a conglomerate of crystals of the monohydratc,

- CaChlLO,

in a matrix of the solidified mother liquor composed substantially of the dehydrate CELGIZ-QH O.

The drying operation has the effect of reduc- 1 ing the water content of the surfaces of the ling than the former product, and ha e less tendency to coalesce and cake in the package.

Another example of a material that may be pr pared in an improved commercial form by means of my improved process is sodium sulphide. The latter compound normally crystallizes from its concentrated aqueous solution in crystals of the composition Na Sflll O, containing from to 33 per cent. anhydrous Na s. A partially dehydrated product, containing the equivalent of to 62 per cent. Na s, is also available commercially, the latter being conveniently prepared by a flaking process, wherein an aqueous sodium sulphide solution is concentrated atatmospheric pressure to a temperature between 170 and 175 C. and then flaked directly. I have found that, upon concentrating still further, for example at, atmospheric pressure to 192 C., a saturated solution is obtained containing approximately 66 per cent. Na S. Such temperature, however, is not readily attainable by means of the usual high pressure steam available for such purposes; It is accordingly preferable to concentrate at a lower temperature under reduced pressure, for example under vacuum at a temperature between 140 and 144 0., in this case continuing evaporation at that temperature, with separation of crystals of anhydrous Na s, until a slurry is formed of highestconsistency that can be handled conveniently by a pump. Such slurry may be flaked much more readily than in the case of the clear solution referred to above, and yields a flake product containing approximately '70 per cent. Nags, being materially enriched in the percentage of anhydrous constituent as compared with the most concentrated product now commercially available.

The concentration of the sodium sulphide under reduced pressure may be carried out satisfactorily under a wide range of pressures and corresponding temperaturesand is not limitedto the preciseconditions just described. In fact, crystals of composition Na -55.911 0, containing about 32 per cent. Nil- S may be melted in their own water of crystallization.- The resulting solution boils at a temperature as low as 110 C. under very high vacuum, and under lower vacuum naturally the boiling point is correspondingly raised. For example, at a pressure of mm. of mercury the boiling point was found to be 1269C, and by continued evaporation under such conditions a slurry of suitable consistency was preparedwhich contained 67st per cent. Na s. When such slurry was flaked, and the resulting flakes were dried and cooled according to the procedure hereinbefore described, a superior product was obtained,'having a materially higher content of anhydrous Nafi than the present 60 to 62 per cent. commercial: product. I lVhile I have described my invention as being particularly applicable to the preparation of a flake product, the advantages in herent in the method of treating a crystal slurry are very apparently of equal applicability to other methods of forming-materials of the character described in divided, comminuted form wherein a suitable slurry treated to produce directly discrete solid particles thereof. For example, a more or less spherical or granular divided form of product may be made by'spraying the slurry from 'a rapidly revolving disc or by forcing it under pressure from an orifice, or by similar methods.

In the following claims, slurry is used to mean a fluid mixture of mother liquor and crystals in suspension therein, having a consistency such that it may be pumped or otherwise handled by means similar to those commonly employed for handling or transferring liquids.

4L nae-am;

' The method. hereindescribed, in. its gem eral. aspeets,zis claimed. in my. copending-"application Serial No..343,96:1.filed Mar-.- 2,1512%... wherein. claims are also included; specific to.

"the" calcium. chloride product and to:- the. method for-the preparation thereof;v Inthe. present application theclaims aredirected specifically to. the sodium. sulphide'prodncti. and to the preparation thereofiin accordance with the. procedure as: set forth..

Other modesof applying the principle of v my invention'mayrbe employed instead ofthe one explained change being made as. re ards the method. herein disclosed, provided; the

step or steps stated by any of the. following; claims or. the equivalent ofsuchstated" step. on steps be employed.

I therefore: particularly point out. and-d-istinctly claim as :my invention 1. .As a new product, a partially. dehydrated sodium sulphide containing substantially more than 62' per cent. anhydrous.- N'a S and imthe form: of" small Eparticles. comprised" an conglomerate of anhydrous Na scrystals in a; matrix. of the I solidified mother liquor thereof, the surfaces offwhichcontain lessv crystal water than, corresponds to the average Water contentof such;partic1'es-..

2. As anew product, a partiallydehydrat ed sodium sulphide containing; substantially more than 62 per cent; anhydrous: Na 'S and. lILtlie form" of flakes comprised. of a. conglomerate of anhydrous Na S'crystails. in' a. matrix of the solidified mother liquor, there 353 of thesurfaces ofwhich contain less crystal. Water than corresponds to' the average. water content of such particles.

3. Asa new product, a: partially dehydrated sodium sulphide containing; approxi- 4oimately 67 to 7 0 per cent. anhydrous-Na san'd in the form of small particlescomprisedoffa conglomerate of anhydrous Na s'crystals in a matrix of the solidified'mother liquorsthere of, the surfaces of which containlss crystal iwater than corresponds to theaveragewater content of such particles.

4.. As a new'product, a partially dehydrats ed sodium sulphide containing-approximately-67 to 70 per cent. anhydrous M1 3 and:

i'in the form of flakes comprised of a conglomerate of' anhydrous Na' S crystals in 0. matrixof the solidified motherliquorthere of, the-surfaces of which contain'less crystal water than corresponds to the'average Water:

; content of such particles.

Signed-by methis 12 day of March; 1929;

Y SHELDON B. HEA:TH1

CERTIFICATE 0F GORREGTIGN.

Patent Ne. 1,843, 767. Granted February 2, 1.932, to

SHELDON B. HEATH.

It is hereby certified that error appears in the printed specification of the abeve numbered patent requiring correction as follows: Page 2, lines 73 and 74, for "flaying" read flaking; tine 8%, {er the inisspeiled werd "anyhtlreus" read anhydrous, and line 93, for "dehydrated" read rtihyttreteti; page 3, time 36, for "dehydrated" read dihyrirateti; page 4, line 34, eiaim 2, strike out the comma after "iiquer" and insert the same after "thereof" lines 34 and 35, same claim; and that the said Letters Patent sheuld he react with these eerreetiens therein that the same may eetrtorm to the reeerd (it the ease in the Patent Office.

Signed and sealed this 12th. day st April, A. D. 1932-.

M. J. Moore, (Seal) Acting Gemtnissioner of Patents.

CERTIFICATE 0F CORRECTION.

Patent No. 1,843,767. Granted February 2, 3.932, to

SHELDON B. HEATH.

it is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as iollows: Page 2, lines 73 and 74, for "flaying" read flaking; line 88, for the misspelled word "anyhdrous" read anhydrous, and line 93, for "dehydrated" read ciiirytlrateti; page 3, line 36, for "dehydrated" read dihytlratetl; page 4, line 34, elaim 2, strike out the comma after "liquor" and insert the same after "thereof" lines 34- anrl 35, same claim; and that the said Letters Patent should he read with these corrections therein that the same may conform to the record of the ease in the Patent Office.

Signed and sealed this 12th day at April, A. D, 1932;.

- M. J. Moore, (Seal) Acting Commissioner of Patents. 

